What Is Frequency in Audio?

Frequency is cycles per second

Sound travels as pressure waves — alternating compressions and expansions in the air. One complete compression and expansion is one cycle. The number of times that cycle happens per second is the frequency, measured in Hertz (Hz). 1 Hz = 1 cycle per second.

The lowest note on a bass guitar vibrates at about 41 Hz — 41 complete cycles per second. Middle A on a piano (A4) vibrates at exactly 440 Hz. The highest note on a piano is about 4,186 Hz. A cymbal crash contains frequencies up to 16,000 Hz and beyond — frequencies you feel as much as hear.

Pitch and frequency are directly related. Higher frequency = higher pitch. Lower frequency = lower pitch. Every musical note corresponds to a specific frequency. When a musician tunes their instrument, they're adjusting the frequency of the vibration.

The audible spectrum

Human hearing spans approximately 20 Hz to 20,000 Hz — though this varies significantly by person and age. Most adults over 40 have meaningful hearing loss above 12–14 kHz. This is relevant to audio engineering because it influences what needs to be preserved in recordings.

What human hearing can and can't perceive

The 20–20,000 Hz range is often cited as the limits of human hearing, but the reality is more nuanced. Sensitivity isn't flat across the spectrum. Human hearing is most sensitive around 2–5 kHz — roughly where speech intelligibility lives. Sensitivity drops off significantly at the very low and very high ends.

This uneven sensitivity is exactly what audio codecs exploit. When an MP3 encoder uses its psychoacoustic model to decide what to discard, high frequencies go first at lower bitrates — because the ears are least sensitive there. Sub-bass also gets reduced. The midrange, where hearing is most acute, is preserved most carefully.

Age matters significantly. Children can hear up to 20 kHz clearly. Most adults over 40 begin to lose meaningful sensitivity above 12–14 kHz. Above 60, the upper limit often drops to 10 kHz or less. Audio engineering content aimed at "hi-res audio" sometimes overlooks this — the frequencies being preserved may already be inaudible to much of the audience.

What frequency range matters for intelligibility

Not all frequencies are equally important for understanding spoken content. The fundamental frequencies of human speech sit between about 300 Hz and 3,000 Hz. The higher frequencies — above 3 kHz — carry consonants: the sounds that distinguish "s" from "sh", "p" from "b", "t" from "d". Without high-frequency content, speech becomes muddy and hard to understand.

Telephone calls are limited to roughly 300 Hz–3,400 Hz — the narrowest range that still allows reasonable speech intelligibility. FM radio extends a bit higher; most broadcast codecs preserve at least up to 15 kHz for music.

For voice recordings — podcasts, audiobooks, interviews — the full audible spectrum isn't critical. Clear capture of the 300 Hz–8 kHz range is the priority. For music, the full spectrum matters: high-frequency content is what gives cymbals their shimmer, instruments their breath, and recordings their sense of space.

Age and hearing range: what this means for quality decisions

The 20–20,000 Hz range is the theoretical maximum for young, healthy human hearing. In practice, most adults progressively lose sensitivity in the upper frequencies with age. By 40, it's common to have significant sensitivity loss above 12–14 kHz. By 60, the upper limit can drop to 10 kHz or lower.

This has practical implications for audio format decisions. The case for high-resolution audio (96 kHz, 192 kHz) often emphasises frequency content above 20 kHz — ultrasonic range that most adults genuinely cannot hear. For the majority of listeners, the audible difference between a 44.1 kHz/16-bit lossless file and a 96 kHz/24-bit file is essentially zero.

For everyday listening, voice content, and distribution: preserving the 20 Hz–16 kHz range accurately is sufficient for virtually all audiences. The top octave of theoretical human hearing is, for most people most of the time, already gone.